For many years people have been trying to create better autostereoscopic three dimensional (3D) displays, and this invention provides a further advance in this field. An autostereoscopic display is a display that gives stereoscopic depth without the user needing to wear special glasses. This is accomplished by projecting a different image to each eye. An autostereoscopic 3D display can be realised by using parallax optic technology such as a parallax barrier or lenticular lenses.
Many applications exist whereby a display is also required to operate in a high quality 2D mode and a high quality 3D mode. For the image display to show an image with 100% native resolution in the 2D mode, the parallax barrier must be switchable between a first mode that provides substantially no imaging function (2D mode) to a second mode of operation that provides an imaging function (3D mode). An example of a liquid crystal switchable parallax barrier technology is disclosed in U.S. Pat. No. 7,813,042B2.
The use of a parallax barrier to direct a different image directly to each eye to create a stereoscopic image for a static, non-moving user is well known. However, the user must remain fixed in space in order to view a high quality 3D image. Movement of the user's head from side to side (lateral movement of the head relative to the display device) causes the left eye image to be viewed with the right eye and vice versa. Viewing the left eye image with the right eye causes severe discomfort to the viewer. In order to solve this problem, a liquid crystal parallax barrier comprising multiple independently addressable electrodes may be used in conjunction with a head tracking system so that for a given viewing distance the left eye image is always directed to the left eye and the right eye image is always directed to the right eye. The head tracking system determines the lateral position of the user's eyes and switches the appropriate electrodes of on the liquid crystal parallax barrier to enable viewing of a stereoscopic image. Examples of such laterally tracking liquid crystal parallax barriers comprising multiple independently addressable electrodes and head tracking systems are disclosed in US20130342586A1, WO000002014136610A1, U.S. Pat. No. 8,629,945B2, US 20120200680A1, US20130342586A1, US20110157171A1, EP00833183A1, US20100110316A1 and U.S. Pat. No. 5,969,850A1.
Other examples of reconfigurable parallax barriers are given in WO 2014/141813, WO 2015/060011, WO 2015/060002, EP1816510, US 2014/198099 and US 2013/021329.
For some applications, particularly on some small displays, a laterally tracked liquid crystal parallax barrier enables sufficient backwards and forwards (longitudinal) movement of the head relative to the display device to enable high quality 3D viewing. However, for other applications, laterally tracking liquid crystal parallax barriers have the disadvantage that movement of the user's head backwards and forwards (longitudinal movement) relative to the display device causes the left eye image to be viewed with the right eye and vice versa i.e. poor quality 3D viewing. U.S. Pat. No. 8,331,023B2 discloses the use of multiple parallax barriers to enable lateral and longitudinal head movement while maintaining good quality 3D viewing. WO2014092172A1, U.S. Pat. No. 8,629,945, US20130187961A1 and US20140078268A1 disclose that a liquid crystal parallax barrier comprised of multiple electrodes can enable lateral and longitudinal head tracking while maintaining good quality 3D viewing. The disclosed method of longitudinal head tracking is performed by changing the pitch of the liquid crystal parallax barrier.